One problem which must be considered before a commercial machine can be released is the provision of a technique for piecing up the yarn to start spinning after an end break.
This problem has been considered by Vyzkumny Ustav Bavlnarsky of Czechoslovakia in their British Pat. No. 2 011 956 and in their U.S. Pat. No. 4 168 601. In both of these patents the yarn is drawn back mechanically by a drawing-in hook moved by the operator and clamped beyond the end of the twisting surfaces. During the movement of the yarn it is under the influence of the suction through one of the surfaces and hence is drawn onto the surfaces.
The problem has also been considered briefly by Dr. Fehrer in his early U.S. Pat. No. 3 635 006. In this technique a seed yarn is drawn back presumably by a drawing-in hook beyond the end of the twisting surfaces into the fibre feed tube. The device shown in this patent has not met with any technical success and has been superceded.
In Japanese patent No. 51-1733 of Toyoda, they propose a technique wherein the yarn end is drawn back presumably mechanically onto a twisting belt with the suction on so that the yarn is drawn into contact with the belt.
Whilst these techniques may be satisfactory in a research environment where only one or a few spinning positions are to be pieced-up, none of them is considered satisfactory for a machine to be sold commercially.